Surgical Techniques and Related Perioperative Outcomes After Robot-assisted Minimally Invasive Gastrectomy (RAMIG): Results From the Prospective Multicenter International Ugira Gastric Registry

OBJECTIVE

To gain insight in global practice of RAMIG and evaluated perioperative outcomes using an international registry.

BACKGROUND

The techniques and perioperative outcomes of robot-assisted minimally invasive gastrectomy (RAMIG) for gastric cancer vary substantially in literature.

METHODS

Prospectively registered RAMIG-cases for gastric cancer (≥10 per center) were extracted from 25 centers in Europe, Asia and South-America. Techniques for the resection, reconstruction, anastomosis and lymphadenectomy were analyzed, and related to perioperative surgical and oncological outcomes. Complications were uniformly defined by the Gastrectomy Complications Consensus Group.

RESULTS

Between 2020-2023, 759 patients underwent total (n=272), distal (n=465) or proximal (n=22) gastrectomy (RAMIG). After total gastrectomy with Roux-en-Y-reconstruction, anastomotic leakage rates were 8% with hand-sewn (n=9/111) and 6% with linear stapled anastomoses (n=6/100). After distal gastrectomy with Roux-en-Y (67%) or Billroth-II-reconstruction (31%), anastomotic leakage rates were 3% with linear stapled (n=11/433) and 0% with hand-sewn anastomoses (n=0/26). Extent of lymphadenectomy consisted of D1+ (28%), D2 (59%) or D2+ (12%). Median nodal harvest yielded 31 nodes [IQR 21-47] after total and 34 nodes [IQR 24-47] after distal gastrectomy. R0-resection rates were 93% after total and 96% distal gastrectomy. Hospital stay was 9 days after total and distal gastrectomy, and was 3 days shorter without perianastomotic drains versus routine drain placement. Postoperative 30-day mortality was 1%.

CONCLUSIONS

This large multicenter study provided a worldwide overview of current RAMIG-techniques with their respective perioperative outcomes. These outcomes demonstrated high surgical quality, set a quality standard for RAMIG and can be considered an international reference for surgical standardization.

Real-world representativeness of patient-reported outcome measures of patients with esophagogastric cancer

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Background: The use of patient reported outcome measures (PROMs) is a popular method to obtain real-world patient data in oncological research. However, PROMs rely on voluntary and active participation of patients and are therefore prone to selection bias. To investigate the suitability of PROMs as real-world data, we investigated the real-world representativeness of the Prospective Observational Cohort Study of Esophageal-Gastric Cancer Patients (POCOP) registry with respect to the Dutch population of patients with esophagogastric cancer. Methods: We identified 2,575 patients in the POCOP registry and 13,702 in the nationwide population-based Netherlands Cancer Registry (NCR) from 2016-2021. We used Representativeness-indicators (R-indicators) to investigate the degree to which the POCOP registry and clinically relevant subgroups thereof, were a representative sample with respect to the population. R-indicators express the representativeness between 0 (not representative) and 1 (perfect representativeness). Calibration methods using inverse propensity weighting were used to correct potential differences between POCOP and the population estimates. Subsequently, median and 5-year overall survival were calculated and compared between patients in the POCOP registry and in the population, to investigate the representativeness in terms of survival. Results: Representativeness of the entire POCOP registry was 0.73 (95% CI: 0.71-0.74). The overall representativeness of palliative patients was higher than that of potentially curable patients (0.89 (0.87-0.90) and 0.70 (0.68-0.71), respectively). Representativeness of most clinical subgroups stratified to treatment was good; R-indicators ranged between 0.8 to 1.0. Median survival of the NCR, POCOP and calibrated POCOP was 19, 32, and 23 months, respectively. The 5-year overall survival of patients in the NCR, POCOP and calibrated POCOP was 26%, 36%, and 27%, respectively. Conclusions: The real-world representativeness of patients who participated in PROMs was good when we accounted for treatment. This shows that in the analysis of PROMs stratification to treatment groups can lead to generalizable results to the population. Using complete non-stratified PROMs, real-world representativeness was lower and calibration methods could be used to correct differences between patients in the PROMs and the population.

Survival expressed in best-case, typical and worst-case scenarios for patients with nonmetastatic esophagogastric cancer: A population-based study

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Background: In recent years new treatment options and the centralization of surgery have improved survival for patients with non-metastatic esophageal and gastric cancer. However, it is currently unknown which patients have mostly benefitted from these treatment advances. The aim of this study was to use population-based data to identify best-case, typical and worst-case scenarios in terms of survival time, and to assess if the survival of these scenarios have changed over time. Methods: Patients diagnosed between 2006-2019 with non-metastatic esophageal (including gastro-esophageal junction tumors) or gastric cancer were selected from the Netherlands Cancer Registry. Best-case, typical, and worst-case scenarios were calculated from the 20th (best-case scenario), 40th (upper-typical), 50th (median), 60th (lower-typical) and 80th (worst-case scenario) percentiles of the survival curves. Linear trend analysis was used to investigate the change in survival time for each scenario across diagnosis years. Results: We identified 23350 patients with non-metastatic esophageal cancer and 10150 patients with non-metastatic gastric cancer. Linear trend analyses across diagnosis years showed that for esophageal cancer patients, survival of all scenarios significantly increased over time: the best-case scenario increased from 55 to 112 months (p =.003); the upper typical increased from 18 to 33 months (p <.001); the median increased from 13 to 23 months (p <.001); the lower typical increased from 8 to 15 months (p <.001) and the worst-case scenario increased from 4 to 7 months (p <.001). For patients with gastric cancer, all scenarios also improved significantly: the best-case scenario increased from 73 to 99 months (p =.045); the upper-typical increased from 22 to 33 months (p <.001); the median increased from 14 to 18 months (p <.001); the lower-typical increased from 14 to 18 months (p <.001) and the worst-case scenario increased slightly from 2.9 months to 3.0 (p =.017). Conclusions: All patients with non-metastatic esophageal and gastric cancer have improved their survival over time.The largest survival advantage was among the best-case and upper-typical scenarios. Therefore, treatment advances over the last years have improved survival for all patients with non-metastatic esophagogastric cancer.

Robotic surgery in emergency setting: 2021 WSES position paper

Background

Robotics represents the most technologically advanced approach in minimally invasive surgery (MIS). Its application in general surgery has increased progressively, with some early experience reported in emergency settings. The present position paper, supported by the World Society of Emergency Surgery (WSES), aims to provide a systematic review of the literature to develop consensus statements about the potential use of robotics in emergency general surgery.

Methods

This position paper was conducted according to the WSES methodology. A steering committee was constituted to draft the position paper according to the literature review. An international expert panel then critically revised the manuscript. Each statement was voted through a web survey to reach a consensus.

Results

Ten studies (3 case reports, 3 case series, and 4 retrospective comparative cohort studies) have been published regarding the applications of robotics for emergency general surgery procedures. Due to the paucity and overall low quality of evidence, 6 statements are proposed as expert opinions. In general, the experts claim for a strict patient selection while approaching emergent general surgery procedures with robotics, eventually considering it for hemodynamically stable patients only. An emergency setting should not be seen as an absolute contraindication for robotic surgery if an adequate training of the operating surgical team is available. In such conditions, robotic surgery can be considered safe, feasible, and associated with surgical outcomes related to an MIS approach. However, there are some concerns regarding the adoption of robotic surgery for emergency surgeries associated with the following: (i) the availability and accessibility of the robotic platform for emergency units and during night shifts, (ii) expected longer operative times, and (iii) increased costs. Further research is necessary to investigate the role of robotic surgery in emergency settings and to explore the possibility of performing telementoring and telesurgery, which are particularly valuable in emergency situations.

Conclusions

Many hospitals are currently equipped with a robotic surgical platform which needs to be implemented efficiently. The role of robotic surgery for emergency procedures remains under investigation. However, its use is expanding with a careful assessment of costs and timeliness of operations. The proposed statements should be seen as a preliminary guide for the surgical community stressing the need for reevaluation and update processes as evidence expands in the relevant literature.

Expectations of Continuous Vital Signs Monitoring for Recognizing Complications After Esophagectomy: Interview Study Among Nurses and Surgeons

Background

Patients undergoing esophagectomy are at serious risk of developing postoperative complications. To support early recognition of clinical deterioration, wireless sensor technologies that enable continuous vital signs monitoring in a ward setting are emerging.

Objective

This study explored nurses’ and surgeons’ expectations of the potential effectiveness and impact of continuous wireless vital signs monitoring in patients admitted to the ward after esophagectomy.

Methods

Semistructured interviews were conducted at 3 esophageal cancer centers in the Netherlands. In each center, 2 nurses and 2 surgeons were interviewed regarding their expectations of continuous vital signs monitoring for early recognition of complications after esophagectomy. Historical data of patient characteristics and clinical outcomes were collected in each center and presented to the local participants to support estimations on clinical outcome.

Results

The majority of nurses and surgeons expected that continuous vital signs monitoring could contribute to the earlier recognition of deterioration and result in earlier treatment for postoperative complications, although the effective time gain would depend on patient and situational factors. Their expectations regarding the impact of potential earlier diagnosis on clinical outcomes varied. Nevertheless, most caregivers would consider implementing continuous monitoring in the surgical ward to support patient monitoring after esophagectomy.

Conclusions

Caregivers expected that wireless vital signs monitoring would provide opportunities for early detection of postoperative complications in patients undergoing esophagectomy admitted to the ward and prevent sequelae under certain circumstances. As the technology matures, clinical outcome studies will be necessary to objectify these expectations and further investigate overall effects on patient outcome.

Intrathoracic versus cervical anastomosis after minimally invasive esophagectomy for esophageal cancer: A randomized controlled trial

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Background: Robust evidence is lacking whether Ivor Lewis minimally invasive esophagectomy (MIE) or McKeown MIE should be preferred for patients with mid to distal esophageal or gastro-esophageal junction Siewert I-II (GEJ) cancer. Methods: In this multicenter randomized controlled trial, patients with esophageal (below the level of the carina) or GEJ cancer planned for curative resection were recruited. Eligible patients were randomly assigned (1:1) to either Ivor Lewis MIE or McKeown MIE. The primary endpoint was anastomotic leakage (AL) requiring endoscopic, radiologic or surgical intervention. Secondary outcome parameters were overall AL rate, postoperative complications, length of stay and mortality. Results: A total of 262 patients were randomly assigned to Ivor Lewis MIE (n = 130) or McKeown MIE (n = 132). Seventeen patients were excluded from the trial due to not meeting inclusion criteria (n = 2), physical unfitness for surgery (n = 3), patients’ choice (n = 3), interval metastases (n = 5) or peroperative metastases (n = 4). AL necessitating reintervention occurred in 15 (12.3%) of 122 patients after Ivor Lewis MIE and in 39 (31.7%) of 123 patients after McKeown MIE (relative risk 0.39, 95% CI 0.22-0.65; risk difference 19.4%, 95% CI 7.9%-31.8%). Overall AL rate was 12.3% after Ivor Lewis MIE and 34.1% after McKeown MIE. Severe complications (Clavien-Dindo ≥ 3b) were observed in 10.7% after Ivor Lewis MIE and in 22.0% after McKeown MIE. Pleural effusion requiring drainage occurred in 9.8% of patients after Ivor Lewis MIE and 21.1% of patients after McKeown MIE. RLN palsy rate was 0% after Ivor Lewis MIE and 7.3% after McKeown MIE. Median length of hospital stay was 10 days (IQR 8 – 15 days) after Ivor Lewis MIE and 12 days (IQR 9 – 18 days) after McKeown MIE. ICU length of stay and mortality rates were comparable between groups. Conclusions: These findings provide evidence for a lower rate of AL requiring reintervention after Ivor Lewis MIE compared to McKeown MIE for patients with mid to distal esophageal or GEJ cancer. Clinical trial information: NTR4333 .

Randomized clinical trial on the effect of a supervised exercise program on quality of life, fatigue, and fitness following esophageal cancer treatment (PERFECT study)

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Background: Patients with potentially curable esophageal cancer are often treated with chemoradiotherapy followed by surgery. This treatment might have a negative impact on physical fitness, fatigue and quality of life (QoL). In patients with other types of cancer, evidence suggests that physical exercise reduces treatment related side effects. We investigated whether a supervised exercise program also beneficially affects QoL, fatigue and cardiorespiratory fitness (CRF) in patients after treatment for esophageal cancer. Methods: The multicenter PERFECT study randomly assigned patients in the first year after esophagectomy to an exercise intervention (EX) or usual care (UC) group. EX patients participated in a 12-week moderate to high intensity aerobic and resistance exercise program supervised by a physiotherapist. UC patients were advised to maintain their physical activity levels. Attendance and compliance with the exercise intervention protocol were retrieved from exercise logs. QoL (primary outcome, EORTC-QLQ-30, range 0-100), fatigue (MFI-20, range 4-20) and CRF (cardiopulmonary exercise testing) were assessed at baseline and after 12 weeks (post-intervention). The outcomes were analyzed as between-group differences using either linear mixed effects models or ANCOVA adjusted for baseline and stratification factors (i.e. sex, time since surgery, center), according to the intention-to-treat principle. Results: A total of 120 patients (age 64±8) were included and randomized to EX (n = 61) or UC (n = 59). Patients in the EX group participated in 96% (IQR:92-100%) of the supervised exercise sessions and compliance with all parts of the exercise program was high ( > 90%). Post-intervention, global QoL was not statistically different between groups, but significant (p < 0.05) beneficial EX effects were found for QoL-Summary scores (between-group difference 3.5, 95% CI 0.2;6.8) and QoL-role functioning (9.4, 1.3;17.5). Physical fatigue wat non-significantly lower in the EX group (-1.2; -2.6;0.1, p = 0.08). CRF was significantly higher (VO2peak (1.8 mL/min/kg, 0.6;3.0) following the EX intervention. Conclusions: Patients were well capable to complete an intensive supervised exercise program after esophageal cancer treatment, which led to small but significant improvements in several aspects of QoL and cardiorespiratory fitness. Our results suggest that supervised exercise is a beneficial addition to routine care of patients with esophageal cancer. Clinical trial information: NTR5045 .

Breath-hold versus mid-ventilation in SBRT of adrenal metastases

PURPOSE

To improve local control in radiotherapy of adrenal metastases precise dose delivery without increasing toxicity is vital. Decreasing the Clinical Target Volume (CTV) - Planning Target Volume (PTV) margins by reducing breathing movement can achieve this. Few data were published concerning the effect of a breath-hold technique. This study investigates the potential of Active Breathing Control (ABC) to limit adrenal breathing movement and reduce CTV-PTV margins.

METHODS

We compared adrenal gland movement in free-breathing, making use of the Mid-ventilation (MidV) technique, and with ABC. The coordinates of the adrenal glands obtained on ten phases of a free breathing 4D-CT and on several repeat inspiration ABC CT-scans were measured. Separate coordinates, the random margin component and the margin vector norm were computed and compared between the two techniques.

RESULTS

We compared the two techniques in 11 patients (21 adrenal glands) and found the largest movement in the Z-direction, with values of 8.7 ± 4.2 mm for MidV and 2.4 ± 1.5 mm for ABC. In 71% of the cases ABC resulted in a smaller margin component than MidV, although non-significant (p ≥ 0.4).

CONCLUSION

Movement of the adrenal gland is largest in the Z-direction. The mean difference in the margin vector norm between both techniques was small with large variations over the patient group, the clinical effect of these differences is unknown. Applying an individualised motion management strategy could be beneficial. If a peak-to-peak amplitude above 15 mm in the Z-direction is observed in the MidV scan we advise to examine if a breath-hold technique could reduce margins.

The Influence of Age on Complications and Overall Survival After Ivor Lewis Totally Minimally Invasive Esophagectomy

BACKGROUND

The number of elderly patients suffering from esophageal cancer is increasing, due to an increasing incidence of esophageal cancer and increasing life expectancy. However, the effect of age on morbidity, mortality, and survival after Ivor Lewis total minimally invasive esophagectomy (TMIE) is not well known.

METHODS

A prospectively documented database from December 2010 to June 2017 was analyzed, including all patients who underwent Ivor Lewis TMIE for esophageal cancer in three Dutch high-volume esophageal cancer centers. Patients younger than 75 years (younger group) were compared to patients aged 75 years or older (elderly group). Baseline patient characteristics and perioperative data were included. Surgical complications were graded using the Clavien-Dindo scale. The primary outcome was postoperative complications Clavien-Dindo ≥ 3. Secondary outcome parameters were postoperative complications, in-hospital mortality, 30- and 90-day mortality and survival.

RESULTS

Four hundred and forty-six patients were included, 357 in the younger and 89 in the elderly group. No significant differences were recorded regarding baseline patient characteristics. There was no significant difference in complications graded Clavien-Dindo ≥ 3 and overall complications, short-term mortality, and survival. Delirium occurred in 27.0% in the elderly and 11.8% in the younger group (p < 0.001). After correction for baseline comorbidity this difference remained significant (p = 0.001). Median hospital length of stay was 13 days in the elderly and 11 days in the younger group (p = 0.010).

CONCLUSIONS

Ivor Lewis TMIE can be safely performed in selected elderly patients without increasing postoperative morbidity and mortality.

Two years' experience with inspiration breath-hold in liver SBRT

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The workflow of inspiration breath-hold SBRT for liver metastases is described.

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Inspiration breath-hold in liver SBRT is feasible for 95% of the patients.

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An individual margin recipe for inspiration breath-hold liver SBRT is explained.

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Margin reduction of 10 mm using inspiration breath-hold compared to free breathing.

Perceived facilitators and barriers to physical exercise adherence in esophageal cancer patients after surgery

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Background: To achieve optimal effects of exercise interventions in esophageal cancer patients, high adherence is needed. Knowledge on facilitators and barriers can help improving exercise adherence. Hence, the aim of this study is to evaluate perceived facilitators and barriers to physical exercise adherence in esophageal cancer patients in the first year after surgery. Methods: Semi-structured interviews were conducted with patients (n = 16) who were randomised to the exercise group of the Physical ExeRcise Following Esophageal Cancer Treatment (PERFECT) Study. Patients participated in a 12-week supervised combined aerobic and resistance exercise program twice weekly, and were advised to be physically active at least 30 minutes each day. Physiotherapists registered attendance at the supervised sessions and compliance (i.e., performing the exercises according to protocol). Transcribed interviews were analysed using a thematic content approach. Results: Median attendance was 97.9%, interquartile range (IQR): 91.7 – 100%. Median compliance to both components of the exercise program was high: 89.6% (IQR 75.5 – 95.8%) for aerobic exercise and 88.0% (IQR 73.8 – 93.6%) for resistance exercise. The most important perceived facilitators were patients’ own attitudes towards exercise (i.e. motivation, commitment and personal goals) and supervision by a physiotherapist. There were only few perceived barriers, of which the most frequently mentioned were logistic factors (i.e. holidays, conflicting activities and weather circumstances) and impaired physical condition due to regular endoscopic esophageal dilation therapy or general physical complaints, such as fatigue. Conclusions: Esophageal cancer patients after surgery are well capable to perform physical exercise with moderate-to-high intensity. The most important perceived facilitators for the high adherence rates are patients’ own attitudes towards exercise and supervision by a physiotherapist. Completion of the exercise program was only minimally affected by perceived barriers as logistic factors and physical complaints. This information can help in designing future exercise programs for clinical practice.

Abstract P2-02-09: The Effect of Breast-MRI in Work-Up of Primary Operable Breast Cancer

Background: Breast magnetic resonance imaging (MRI) is becoming an often-utilized examination in the preoperative planning for breast cancer. However, it is not yet accepted as a routine examination for all breast cancer patients due to the lack of data regarding whether breast MRI has any effect on recurrence or survival.

Aim: The aim of this study is to evaluate the effect of MRI on surgical management in operable breast cancer.

Methods: From April 2008 till January 2010 consecutive primary operable breast cancer patients had a preoperative breast-MRI in addition to regular mammography and ultrasonography. Additional lesions newly found by MRI were evaluated with a target ultrasound and if needed biopsied. Moreover MRI tumor size was compared to mammographic and ultrasonographic tumor size.

Blinded for MRI results and the performed surgical plan, surgical management based on traditional radiological work-up was determined retrospectively by 2 surgeons. Change of surgical plan by MRI was subsequently analysed. Accuracy of MRI based surgical plan was evaluated by comparing definitive pathology.

Results Hundred ninety eight consecutive patients were analyzed. Median age was 59 years (23-82). Additional ipsilateral and contralateral suspicious lesions were detected by MRI in 53 patients (27%). Twenty two patients had additionally target-ultrasonography: 5 lesions were not found, 4 lesions had benign aspect. Five out of 13 biopsied patients had second breast cancer, 3 patients had contralateral breast cancer and 2 patients had multicentric breast cancer. In 31 patients no further evaluation was performed because the new focus was supposed to be a satellite (n=12) or mastectomy was already chosen to be done (n=19). There was a change in surgical plan due to MRI results in 35 of 198 patients (18%), all of whom received more extensive surgery than previously planned: in 17 patients mastectomy was performed instead of lumpectomy, 15 patients had a more extensive lumpectomy. Three patients had contralateral surgery for breast cancer.

In 24 patients (69%) MRI based surgical plan was confirmed by definitive pathology. In 11 patients MRI overestimated tumor size or misinterpreted a satellite lesion.

Conclusion. Breast MRI contributes to a significantly change of surgical plan. However, false-positive findings are frequent. Therefore, in unselected primary operable breast cancer patients routine implementation of breast MRI is not right away justified.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-02-09.

Monte Carlo dosimetry of a new 192Ir pulsed dose rate brachytherapy source

A new microSelectron pulsed dose rate source has been designed, containing two active pellets instead of one inactive and one active pellet contained in the old design, to facilitate the incorporation of higher activity up to 74 GBq (2 Ci). In this work, Monte Carlo simulation is used to derive full dosimetric data following the AAPM TG-43 formalism, as well as the dose rate per unit air kerma strength data in Cartesian, "away and along" coordinates for both source designs. The calculated dose rate constant of the new PDR source design was found equal to lambda=(1.121 +/- 0.006) cGy h(-1) U(-1) compared to lambda = (1.124 +/- 0.006) cGy h(-1) U(-1) for the old design. Radial dose functions of the two sources calculated using the point source approximated geometry factors were found in close agreement (within 1%) except for radial distances under 2 mm. At polar angles close to the longitudinal source axis at the sources' distal end, the new design presents increased anisotropy (up to 10%) compared to the old one due to its longer active core. At polar angles close to the longitudinal source axis at the sources' drive wire end however, the old design presents increased anisotropy (up to 18%) due to attenuation of emitted photons through the inactive Ir pellet. These differences, also present in "away and along" dose rate results, necessitate the replacement of treatment planning input data for the new microSelectron pulsed dose rate source.

Geometrical reconstruction of images obtained with electronic endoscopy

We use an electronic video endoscope (Fujinon EG7-HR2) to image the mitral valve in situ in an isolated pig heart preparation. From video recordings, images are digitized and analysed with a computer. A complication encountered during the study concerned the geometric wide angle distortion caused by the device. The present paper describes a method developed to reconstruct the image, and to correct for this distortion. In order to quantify the relation between object and image, model equations were formulated based on mild assumptions. Points in object space are transformed through a non-linear relation to corresponding points in image space. Furthermore, an oblique camera view, and an aspect ratio correction factor, are accounted for. As a test object, a regular grid of points was recorded at several distances from the camera. The images of the grid points were digitized, and the model equations were fitted to these data. From test measurements, carried out in air as well as in water, it was concluded that the distortion could be quantified by three parameters. Application of the straightforward correction procedure enables us to obtain quantitative information from endoscopic images.

Retrograde coronary flow is limited by time-varying elastance

The study examined the influence of left ventricular pressure (PLV) on coronary arterial flow and pressure. In eight anesthetized open-thorax goats with cannulated and artificially perfused left main coronary artery, the PLV was disturbed by aortic occlusions. In the constant pressure perfusion (CPP) protocol the response of systolic arterial inflow on a change in PLV was studied with fixed perfusion pressure and at several perfusion pressure levels. Similarly, in the constant flow perfusion (CFP) protocol the response of systolic perfusion pressure was examined with fixed levels of perfusion flow and repeated for several flow levels. The results show an early systolic response determined by PLV for both protocols. Midsystolic responses were almost absent in the CPP protocol but present in the CFP protocol. At CPP, the effect of a change of PLV on arterial flow in mid systole was only 20% of that on early systolic flow with intact coronary tone and 33% with adenosine-induced vasodilation. At CFP the pulsations in perfusion pressure were 30% of PLV pulsations, both with intact tone and vasodilation; in contrast with the CPP results, no difference for this value was found in different stages of systole. We suggest that stiffness of cardiac muscle determines the influence of PLV on coronary flow. The difference in mid systolic relations between the CPP and CFP protocols is explained by the difference in time constants induced by the perfusion system. The results are best explained by a synthesis between the intramyocardial pump model and the elastance concept.

Mechanics of the patellar articulation. Effects of patellar ligament length studied with a mathematical model

We investigated the influence of the length of the patellar ligament on (1) the relative positions of the ligament, patella, and quadriceps tendon, (2) the location of the patellofemoral contact point, (3) the force of the quadriceps femoris muscle, and (4) the patellofemoral compression force for 0-120 degrees flexion-extension angles of the knee. For this purpose, we used a mathematical model, describing movements and forces in the sagittal plane. The anatomic parameters for the model were obtained from five autopsy knees. The patellar ligament length appeared to influence the mechanical behavior of the patellar articulation considerably. The magnitude of the induced changes was determined by the length of the ligament and by the flexion-extension angle of the knee.

The influence of anterior displacement of the tibial tuberosity on patellofemoral biomechanics

The effect of anterior displacement of the tibial tuberosity at distances of 5, 10, 15 and 20 mm on the mechanical behaviour of the patellofemoral joint has been investigated using a mathematical model, which describes movements and forces in the sagittal plane. Anatomical parameters for the model were obtained from five normal autopsy knees. The results show that anterior displacement: 1) increases the length of the contact paths on both patellar and femoral articulating surfaces, 2) produces a lengthening of the moment arm of the patellar ligament force, 3) may either decrease or increase the ratio between patellar ligament force and quadriceps muscle force and 4) decreases the ratio between patellar compression force and quadriceps muscle force. The magnitude of these effects depends on the flexion-extension angle of the knee and the displacement distance of the tibial tuberosity.

Forces acting on the patella during maximal voluntary contraction of the quadriceps femoris muscle at different knee flexion/extension angles

From knee extension moments measured with a dynamometer, the quadriceps muscle force, the patellar ligament force and the reaction force in the patellofemoral joint at various knee angles (0-90 degrees) were estimated. The information needed to calculate the combined effect of both patellofemoral and tibiofemoral joint on the mechanical advantage of the muscle was obtained from lateral-view radiographs of autopsy knees. The results show that the smallest quadriceps force (2,000 N) is exerted at maximal extension, and the largest force (8,000 N) at about 75 degrees of flexion. The patellar ligament force reaches a maximum (5,000 N) at 60 degrees. The reaction force in the patellofemoral joint is the smallest (1,000 N) at extension and is of the same values as the muscle force in a range from 75 to 90 degrees. Especially at large flexion angles, the value of the estimated forces is considerably larger (by 100%) than reported in the literature. This difference is attributed to the influence of the patellofemoral joint on the mechanical advantage of the muscle, which has not been taken into account in other studies.

A mathematical model of the patellofemoral joint

A mathematical model of the patellofemoral joint taking into account movements and forces in the sagittal plane is described. The system parameters of the model are the locations of the attachments of the quadriceps muscle and the patellar ligament, the length of the patellar ligament, the dimensions of the patella and the geometry of the articulating surfaces. They were obtained from ten autopsy knees. The model enables calculation of the relative position of the patella, patellar ligament and quadriceps tendon, the location of the patellofemoral contact point and the magnitude of the patellofemoral compression force and the force in the patellar ligament as a function of the location of the tibial tuberosity at different flexion-extension angles of the knee. The model is validated by comparing model data with experimentally determined data.